I'm on my fourth child. Every pregnancy is different. I felt my first around 22-25 weeks. My second at 15 weeks my third at 28 weeks and I'm 20 weeks right now and have not felt movement but hear the heart beat at every appointment:)
Also, if your placenta is at the front of the uterus, he or she has to kick so hard that you feel it through it. I'm 21+1, and don't feel all the movement a lot of others do for that reason. But the bubly feeling that you probably feel every now and then? That's probably it.
You will have to concentrate to feel any movement . Even I thought same and thought it's all gas, but my friend suggested that those butterfly movements is baby . Now I can feel by just keeping my palms on my tummy and concentrating lil bit. You will feel that baby is moving inside you ..